Automotive Mechatronics - Automotive electronics is becoming a fundamental feature of modern cars, especially cars. As an important part of automotive electronic control, engine electronic control has been highly valued by domestic and foreign automobile manufacturers in order to adapt to increasingly strict emission and safety regulations, and has achieved unprecedented development.
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I. Overview
The theoretical basis of modern car electronic control technology is modern control theory. From the early classic control to the current intelligent control, the control theory has been widely used in automotive electronic control. There are mainly PID control, optimal control, adaptive control, sliding mode control, fuzzy control, neural network control and predictive control. The development of modern control theory makes the electronic control system more adaptable to complex multivariable systems, time-varying systems and nonlinear systems, and even accurate and effective control for systems with less accurate mathematical models. This is the premise that the electronic control of the engine can be realized. In terms of its structure, the electronic control system is mainly composed of three parts: a sensor, an electronic control unit (ECU) and an actuator. The sensor is used as an input part for measuring physical signals (temperature, pressure, etc.) and converting it into an electrical signal; the function of the ECU is to receive the input signal of the sensor, and perform calculation processing according to the set program, and output the processing result; the actuator The actuator is driven according to the electrical signal output by the ECU to change as required.
(1) Electronic Control Component (ECU)
The ECU is centered on the microcomputer. It also includes a pre-A/D converter, a digital signal buffer, and a post-signal amplifier. The microcomputer has fast calculation speed, high precision, real-time control, and multi-interrupt response. At present, in addition to 8-bit and 16-bit microcomputers, 32-bit, especially 64-bit microcomputers have begun to be gradually used. Moreover, not only general-purpose microcomputers and single-chip microcomputers, but also specialized automotive microcomputers have been developed. It is the rapid development of microcomputer technology that has promoted the continuous improvement of automotive electronic control technology. It can be said that the current general trend of ECU development is the transition from single-system single-machine control to multi-system centralized control. Soon after, the automotive electronic control system will use computer network technology to connect the ECUs of the engine electronic control system, the body electronic control system, the chassis electronic control system and the information and communication system to form a distributed computer network within the machine. Comprehensive control of automotive electronics.
(two) sensor
Automotive sensors have extremely harsh operating conditions, so it's critical that the sensors work accurately and accurately. In recent years, theoretical research and material application development have been rapid in this field, and semiconductor and metal film technologies and ceramic sintering technologies have developed rapidly. Undoubtedly, intelligence, integration and digitization will be the future development trend of sensors.
(three) actuator
The actuator is used to execute the command signal from the ECU accurately and without error. Therefore, the accuracy of the actuator work will ultimately affect the success or failure of electronic control, which is why its work reliability and accuracy have always been the focus of research. At present, there are many types of actuators for automotive electronic control systems, such as solenoid valves, electric motors, piezoelectric components, igniters, electromagnetic relays, thermocouples, etc., and their structures and functions are not the same. The development of actuators is intelligent actuators and solid state intelligent power units.
Second, the engine electronic control technology and application
Engine electronic control technology can be divided into electronically controlled gasoline injection, electronic ignition, idle speed control, exhaust gas recirculation control, boost control, fault self-diagnosis, fault insurance, standby control and other control technologies.
(1) Electronically controlled gasoline injection (EFI) system
The electronically controlled gasoline injection system (referred to as the EFI system) was developed in the late 1960s. Compared with the carburetor fuel supply system commonly used in the early days, the outstanding advantage is that the air-fuel ratio control is more precise and the best air can be achieved. Burning ratio; and EFI technology improves the atomization and evaporation performance of gasoline, and the acceleration performance is better, and the engine power and torque are significantly increased.
At present, the EFI system mainly adopts a combination of open loop and closed loop control (feedback control). Open-loop control is performed for conditions such as warm-up, idle speed, etc., which are required to supply a rich mixture. In addition, the actual air-fuel ratio is measured by an oxygen sensor provided in the exhaust pipe to perform feedback control. The air intake meter or the intake manifold absolute pressure sensor and the speed sensor measure the intake air amount, and the ECU determines the appropriate air-fuel ratio according to the cooling water temperature, the intake air temperature, the oxygen sensor signal, etc., and calculates the required fuel injection amount, and then The actuator (injector and circuit disconnect relay) is controlled. The EFI system can be divided into three types according to the installation position of the injector: single injection (SPI), multi-point injection (MPI) and direct injection in the cylinder. Single-point injection is installed at the intake pipe throttle with 1 or 2 injectors. Multi-point injection installs each injector separately in the intake manifold of each cylinder, so that the mixture distribution of each cylinder is relatively uniform, so it is widely used in cars. Moreover, according to the difference of fuel injection timing, the multi-point injection can be subdivided into three types: simultaneous injection, group injection and sequential injection. The sequential injection enables the injector to spray according to the ignition sequence of each cylinder. Once, this method works better than the first two applications. In-cylinder direct injection, especially the four-stroke gasoline engine direct injection in the cylinder is the cutting-edge technology in the current gasoline injection of cars. It was first developed by Mitsubishi Corporation of Japan. The injector is installed on the cylinder head and directly injects gasoline into the cylinder during operation. Perform mixed combustion. The realization of the direct injection technology greatly reduces the fuel consumption of the gasoline engine, and the power performance is also more excellent. At the same time, with other mechanisms, the high air-fuel ratio lean combustion technology can be realized.
(2) Electronic ignition control system
As early as the beginning of the 20th century, ignition systems have been applied in automotive engines, from contact-type, general non-contact, integrated circuit, to today's microcomputer-controlled electronic ignition systems. The microcomputer-controlled electronic ignition system can control and maintain the engine ignition advance angle (ESA) within the optimal range, making the gasoline engine's ignition timing closer to the ideal state, further digging the engine's potential.
In the microcomputer-controlled ignition system, a distributorless ignition (DLI) system has emerged, which eliminates the distributor in the ordinary microcomputer-controlled ignition system, and the internal control of each cylinder is controlled by the ECU. In this way, the high-voltage electricity generated by the ignition coil is directly sent to the spark plug for ignition without being distributed by the distributor. The distributorless ignition system can eliminate the spark discharge phenomenon of the electrodes on the edge of the splitter and the distributor, and reduce electromagnetic interference. The distributorless ignition system has two cylinders simultaneously igniting and two cylinders independently igniting according to the different ignition sequence. In the two-cylinder simultaneous ignition mode, one ignition coil is used for each of the two cylinders, and all the cylinders are divided into groups and fired in groups; in each cylinder independent ignition mode, each cylinder's spark plug is provided with a separate ignition coil. (In particular, with the appearance of the ignition coil of the ultra-small plastic package, it is integrated with the spark plug), so that the cylinders can be ignited in turn.
In the ignition control of the engine, a combination of open loop and closed loop control is also adopted. The ignition timing of the starting phase is controlled by the special signal in the ECU. During normal operation, the knocking feedback control is performed by adding a knocking sensor, and the ignition timing is adjusted according to the feedback signal of the knocking sensor to make the engine in a critical knocking state.
(3) Idle speed control (ISC) system
The performance of idle speed is an important indicator to evaluate the superiority of engine performance. The poor idle performance will lead to increased fuel consumption and serious sewage discharge. Therefore, necessary control is required. Modern cars usually have an idle speed control system that is controlled by the ECU and maintains the engine idle speed within a certain stable speed range. Therefore, the idle speed control usually refers to the idle speed control, and the essence thereof is to adjust the intake air amount in the idle condition (at the same time, the injection amount and the ignition advance angle are controlled). The basic principle of the idle speed control is that the ECU calculates the target speed based on the cooling water temperature, the air conditioning load, the neutral signal, etc., and compares it with the actual speed, and simultaneously detects the throttle full off signal and the vehicle speed signal to determine whether it is in an idle state. The difference between the target speed and the actual speed drives the actuator to adjust the amount of intake air.
At present, in addition to the stability control of the idle speed, the idle speed control can also implement functions such as start control, warm-up control, and load change control, so that the concentration of multiple functions not only simplifies the mechanism but also improves the accuracy of the idle speed control. Sex.
The idle speed control system can be divided into two types: the throttle direct-acting type and the bypass air type according to the different control methods of the intake air quantity. The latter has a wide application, and the actuator-idle speed control valve develops faster, correspondingly has steps. Into the motor type, rotary solenoid type, duty cycle type and switch control type, each has different degrees of application in idle speed control.
(4) Exhaust gas recirculation (EGR) electronic control system
Early studies abroad have found that a small amount of exhaust gas (5% to 20%) is recirculated into the cylinder and mixed with fresh combustible gas mixture, which can effectively suppress NOx production. In fact, in addition to the internal EGR method that can generate exhaust gas recirculation by valve overlap, a more common measure is to use a special pipe to lead part of the exhaust gas to the intake pipe, and the ECU controls the EGR valve to change the flow cross section to adjust the exhaust volume. A change in the recirculation rate is achieved. It is usually not necessary to perform EGR control in conditions such as engine warm-up, idle speed, low load, and high load.
The general process of EGR control is: ECU calculates the optimal recirculation exhaust rate based on the engine speed, throttle opening, cooling water temperature and other signals, and then achieves EGR control by controlling the opening of the EGR valve. The ECU's control of the EGR valve is essentially achieved by controlling the vacuum regulator valve. The vacuum regulating valve is generally electromagnetic and is used to convert the electrical signal output by the ECU into a pressure change, thereby realizing the control of the pneumatic EGR valve. And, the ECU also performs feedback control by measuring the recirculation exhaust rate signal through a pressure sensor. In the implementation of feedback control, the independent pressure or differential pressure sensor was used initially, and now the EGR position sensor integrated with the EGR valve has appeared to improve the control accuracy.
(5) Supercharged electronic control system
The installation of the booster system in the engine is increasing, and the purpose is to improve the intake efficiency. The development of the electronically controlled supercharging system has brought the supercharging technology to a new level. At present, the most common application is the electronically controlled exhaust gas turbocharging system. Usually, the supercharger is designed to match the engine's low speed and low load conditions. When the engine is under heavy load, it is easy to cause the supercharger to overspeed and damage. For this reason, the electronically controlled exhaust turbocharger system is specially used in the exhaust pipe. A side air passage is added to the middle exhaust gas turbine chamber, and the opening degree of the switching valve is controlled by the ECU to adjust. Normally, the switching valve is closed and the exhaust gas is exhausted through the turbine air chamber. Once the engine is under heavy load, the exhaust gas turbine speed will increase. When the intake pressure exceeds the limit value, the ECU will open the switching valve through the corresponding mechanism to make the bypass air passage guide. The exhaust gas is directly discharged from the bypass air passage without passing through the turbine chamber, and the supercharger stops working.
(6) Fault self-diagnosis system
In the electronic control system of modern car engines, ECUs generally have fault self-diagnosis systems to monitor and diagnose faults in various parts of the engine control system. For the sensor, it can be directly judged by detecting whether the signal is out of the specified range; for the actuator, a special circuit is added to the initial circuit to realize the monitoring, and for the ECU itself, there is also a dedicated program for diagnosis.
The fault self-diagnosis system monitors the working conditions of each control system at all times. When a fault occurs, the fault indicator light on the general car dashboard can flash alarm, and the fault information is saved in the memory of the microcomputer in the form of code. It can be displayed by intermittently flashing the fault indicator. The fault code can also be displayed in digital form by a dedicated test instrument to further identify the cause of the fault through the manual. The self-diagnosis system solves the problem that it is difficult to judge faults in complex electronic control systems.
(7) Fault insurance system and fault standby control system
When the self-diagnostic system detects the sensor and its circuit failure, the fail-safe system in the ECU automatically starts to function. The fail-safe system replaces the abnormal signal input in the fault part with the data set by the program for direct control. The fail-safe system is typically implemented by software programming.
When the microcomputer or the main sensor (such as the intake manifold pressure sensor) fails, the ECU immediately switches the master control from the microcomputer to the fault backup system, which replaces the microcomputer. As an integrated circuit module of the ECU, the fault backup system can only determine the simplest control scheme for maintaining the running of the vehicle according to the starting signal and the idle contact status signal, ensuring that the car “slows home†for repair, but cannot achieve microcomputer control. The best performance at the time.
(8) Other electronic control systems
1. Intake vortex electronic control system intake vortex can promote gasoline evaporation and uniform mixing with air, improve combustion efficiency. Electronically controlled intake eddy currents are used in some cars (especially those with lean-burn technology). The structure is that an eddy current control valve is added near the air inlet, and the ECU collects signals such as the rotational speed, the throttle opening degree, the cooling water temperature, and the like, and controls the rotation angle thereof, guides the airflow deflection to generate the eddy current, adjusts the eddy current ratio, and realizes the eddy current. control.
2. Variable intake control system The variable intake control system improves engine power performance from the perspective of increasing intake air intake and improving intake efficiency. There are two types of system: one is variable flow area control. In the way, the ECU controls the rotation angle of the control valve installed in the intake pipe to change its intake flow cross section to meet the demand for the intake air volume under different working conditions; the other is the variable circulation length control mode by the ECU The control valve in the intake duct is controlled to adjust the length of the intake pipe. It has been proven that the variable intake control system enhances engine power and economy.
3. Intake air temperature preheating control system The intake air temperature preheating control system promotes gasoline evaporation and improves emission performance by adjusting the intake air temperature at low temperature starting. Preheating methods mainly include exhaust pipe preheating, water temperature preheating and positive temperature component (PTC) preheating.
4. Fuel Evaporation Electronic Control System The fuel evaporative electronic control system is used to reduce the pollution caused by the discharge of gasoline vapor into the atmosphere in the fuel tank. At present, the activated carbon tank evaporation electronic control device has been widely used. During the parking period, the activated carbon tank is used to absorb the gasoline vapor to prevent diffusion into the atmosphere; after the engine is running, the ECU controls the conduction between the activated carbon canister and the intake pipe, and the gasoline vapor adsorbed in the activated carbon canister is sucked into the intake pipe by the intake vacuum degree, so that It can effectively prevent the escape of gasoline vapor and reduce the pollution of HC emissions.
5. Crankcase forced air control system The purpose of the crankcase forced air control system is to recirculate the gas in the cylinder through the piston ring clearance into the crankcase to reduce the direct discharge of the gas to the atmosphere. Pollution. In the modern electronic control system, the ECU controls the forced ventilation valve according to the throttle position signal, the rotational speed signal, etc., thereby achieving conduction between the gas in the crankcase and the intake pipe, and then utilizing the gas in the crankcase.
6. Secondary Air Injection System Secondary air injection is one of the early measures to control pollutant emissions and is currently used in conjunction with catalytic converters. It is also controlled by the ECU to control the conduction of the secondary air injection air passage, and introduces air into the catalytic converter to realize the conversion of NOx, CO, and HC. In the manner of introducing air into the exhaust pipe, in addition to the air pump control, exhaust pulse waves can be used. In addition, as the research progressed further, many new technologies emerged. Such as cylinder deactivation control, it can stop the fuel supply and ignition control of some cylinders according to the different requirements of the load, reduce waste and improve engine efficiency; like the accelerator pedal electronic control system, it can avoid the error caused by the mechanical accelerator pedal due to wear. , increase control accuracy.
Third, the conclusion
With the improvement of microcomputers and electronic technologies and the vigorous development of materials technology, coupled with the continuous maturity of control theory, engine electronic control technology is expected to achieve greater breakthroughs.
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